Aug 4, 2011 (CIDRAP News) – Federal officials reported today that ground turkey products belonging to two patients in the current multistate Salmonella outbreak were traced to a Cargill Inc. facility on Jul 20, 2 weeks before investigators presented all their evidence to the company, prompting yesterday's Cargill recall of 36 million pounds of ground turkey.

But in a press conference, officials from the US Department of Agriculture (USDA) and the Centers for Disease Control and Prevention (CDC) defended their response to the outbreak, saying the picture wasn't clear enough to tie the outbreak to the Cargill facility in Arkansas until very recently.

They said the picture was muddied by the small number of cases clearly linked to Cargill and by signs that turkey products from some other companies might have been involved. Also, it took until Jul 29 to confirm the outbreak strain of Salmonella in an open package of ground turkey from one of the patients.

As of today the outbreak includes 78 cases in 26 states, with 22 hospitalizations and one death, said Chris Braden, MD, director of the CDC's Division of Foodborne, Waterborne, and Environmental Diseases. He said onset dates for confirmed cases range from Mar 9 to Jul 2, but there may be other cases not yet reported.

Late yesterday Cargill announced the recall of almost 36 million pounds of fresh and frozen ground turkey products from a company facility in Springdale, Ark., because of possible links to the outbreak. The recall applies to products produced from Feb 20 through Aug 2.

Federal officials said today they believe the recall is the third-largest meat recall in US history.

The chronology of the outbreak investigation was traced by Braden and David Goldman, MD, assistant administrator of the Office of Public Health Science in the USDA Food Safety and Inspection Service (FSIS).

"This was a slowly building outbreak in the beginning," said Braden.

Officials began investigating an unusual cluster of cases of Salmonella Heidelberg, an antibiotic-resistant strain, on May 23, he said, but the initial interviews with patients did not support a connection to ground turkey.

Meanwhile, a few retail samples of ground turkey that were tested in routine surveillance by the CDC's National Antimicrobial Resistance Monitoring System (NARMS) were positive for the Salmonella Heidelberg outbreak strain, Braden said. These showed up at the rate of one per month from April through July. In response to questions, he said these four samples were traced to the Cargill plant in Arkansas.

The NARMS findings spurred more intensive questioning of case-patients about exposure to turkey, which eventually led to the finding of a link, he said.

Eventually the investigators found three patients who had Cargill ground turkey products in their possession. Goldman said. The FSIS began trace-back activity on two cases from one state on Jul 18, and within 2 days the agency confirmed that their products came form the Cargill facility in Arkansas, he said.

"The investigation into the third case was begun Jul 26, and a similar verification of the purchase of product was made 2 days later," Goldman said. He added that "shopper card" information on the patients' food purchases was very helpful in gathering the evidence.

Braden said the products from patients' homes that were linked to Cargill on Jul 20 were tested, leading to confirmation of the outbreak strain in one of the samples on Jul 29.

In response to questions, Goldman said FSIS first contacted Cargill about the outbreak on Friday, Jul 29, when it had "preliminary discussions" with company legal representatives. "We've been in communication with them since then. It was only yesterday that we presented the full set of facts . . . to not only their legal representative but their corporate management as well," he said.

One factor, he said, was that "we were provided a line listing of cases who reported ground turkey exposures, and there quite a few non-Cargill exposures." He later commented that those links "don’t have the same level of evidence as for the Cargill plant," but that could change.

"The other issue we have is we're focusing on three cases at the time out of 77. That's a difficult issue to weigh," Gold man said. "We have to determine that we have enough information to take forward to the company, even though we can't explain the vast majority of cases."

In other comments, he said, "We confirmed the trace-back information last week for the most part." Also, the FSIS needed to corroborate the trace-back findings with findings from the Cargill plant, he added.

Goldman said the FSIS is sure that the Cargill facility is the source of the outbreak, but it's not yet known exactly how contamination occurred there.

He said poultry plants are tested "periodically" for Salmonella, a very common pathogen that is not classified as an adulterant in poultry meat. The last round of testing at the Arkansas plant was in 2010. "In 2010 there were three positive Salmonella Heidelbergs among the positives in that set," he said.

Investigations are still under way at the Cargill plant, Goldman said. "What we have, the trace-back confirms that products that patients purchased that made them sick with Salmonella Heidelberg originated in that plant. That's the key fact."

In other questioning, a reporter asked why the NARMS findings of retail turkey samples that came from the Cargill plant and had the outbreak strain didn't prompt an investigation of the facility much earlier.

Braden replied that it's true that the retail samples had a Salmonella Heidelberg strain that could be linked to some patients through PulseNet, the CDC database of pathogen DNA fingerprints. However, he added, "The retail meat that was tested was not linked to illness that we know of in any way. And it is true that if you test poultry meat, you may find Salmonella."

Further, he said the NARMS findings did prompt investigators to adopt a possible turkey source as their "primary hypothesis" in the investigation. "When we did that at the beginning of this investigation, we actually were not finding a significant proportion of those cases that had turkey meat exposure. So we were finding dissonant types of information that I think prevented us from acting at that point. And we then had to go on to collect additional information to bring it all together."

One reporter asked Goldman to comment on the use of irradiation to control contamination to prevent outbreaks like the current one. He replied briefly: "FSIS has approved the use of irradiation, and it's really up to individual plants or processing facilities to decide to use it."